Hydraulic tappet



July 24, 1956 s. OLDBERG HYDRAULIC TAPPET 2 Sheets-Sheet 1 Filed Sept. 10, 1952 LIE-i INVENTOR. Smuev OLDBERG ATTORNEYS CHECK VAL r5 Z/Fr Loss July 24, 1956 s. OLDBERG 2,755,785

HYDRAULIC 'IAPPET I Filed Sept. 0. 1952 2 Sheets-Sheet 2 CHECK Mia/E Z/Fr Lass CHECK Mia/E TRAVEL I I a I a l 1 O .002 004 .ooe .008 .0/0 .0/2 .0/4 .0/6 .016

CHECK Mal/E 75/71 51.

E 15 7 INVENTOR.

SIDNEY OLDBERG MM. Mag,

A TTOKNE Y5 2,755,785 Patented July 24, 1956 HYDRAULIC TAPPET Sidney Oldberg, Birmingham, Micln, assignor to Eaton Manufacturing Company, Cleveland, Ohio, a corporation of Ohio Application September 10, 1952, Serial No. 308,887

1 Claim. (Cl. 123-90) This invention relates to valve gear systems for internal combustion engines and more particularly to hydraulic tappets therefor.

Broadly the invention comprehends the provision of hydraulic tappets for use in valve gear systems of internal combustion engines effective to automatically compensate for variation in the operating length of said valve gear systems, wherein the tappet employs a flat check valve and specific physical proportions are maintained among the essential elements thereof providing for a controlled amount of lift loss.

Although a great number of hydraulic tappets have been devised having lift loss operating characteristics, none have provided for simply and easily obtaining a controlled amount of lift loss.

Among the objects of this invention is the provision of a hydraulic tappet employing a fiat check valve, that:

l. is designed to provide a controlled amount of lift loss;

2. Incorporates structure therein for easily, simply and economically providing for a controlled amount of lift loss;

3. Provides for a controlled amount of lift loss by way of a proper physical proportioning of the basic elements thereof relative to one another; and

4. is designed according to a predetermined formula of comparative physical size and distance of movement of predetermined elements of the tappet to insure controlled lift loss operation thereof.

Other objects and advantages of the invention will appear from the following description taken in connection with the drawings forming a part of the specification, and in which:

Fig. l is a vertical cross-sectional view of a hydraulic tappet embodying the invention;

Fig. 2 is a top elevation view of Fig. 1;

Fig. 3 is a cross-sectional view taken substantially along lines 33 of Fig. l; p

Fig. 4 is a cross-sectional view taken substantially along lines =i-l of Fig. 1;

Fig. 5 is an enlarged fragmentary view of the valve mechanism of Fig. 1;

Fig. 6 is a graph of lift loss plotted against check valve travel; and

Fig. 7 is a graph of lift loss plotted against check valve travel for tappets having varied plunger diameters.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

This hydraulic tappet was devised for the purpose of providing a tappet having a controlled lift loss and wherein the lift loss is predeterminedly based upon the proportionate sizes of various elements of the tappet and the travel of the check valve of the tappet. The basic elements of the tappet, the plunger, and check valve, enter into the utilization of a formula for predetermining lift loss operation of the tappet, wherein the check valve used is of a flat generally circular variety. The area of the plunger, check valve and opening controlled by the valve and the travel of the check valve together with a predetermined constant of .27 are factors employed in the formula for a desired lift loss. Lift loss as applied to the valve gear systems of internal combustion engines and particularly as regards automatic length compensating means, such as hydraulic tappets, employed in said valve gear systems, means the amount of clearance that is positively introduced in the lineal operating length of a valve gear system so as to insure against a valve remaining open after a complete cycle of operation thereof. In predetermining the lift loss to be introduced into a specified gear system, an effective and eflicient operation is achieved without chance of malfunctioning thereof.

Referring to the drawings for more specific details of the invention 10 represents generally a hydraulic tappet for incorporation in a valve gear system for internal combustion engines between a cam and pushrod, not shown. As shown by Fig. 1, the tappet is in its fully expanded condition. I

Tappet 10 comprises basically a hollow cylindrical body 12 closed at one end 14, a plunger 16 reciprocable in the hollow of the body, a circular flat check valve 18, a valve cage 20 and a spring 22.

A spring clip 24 is appropriately seated in an annular groove 26, on the internal peripheral wall of the body 12, near the open end thereof, for limiting the outward axial movement of the plunger.

Plunger 16 consists of two parts, a sleeve member 28 and a cap member 30 appropriately arranged in inserted relation on one end 32 of the sleeve.

Sleeve member 28 is reciprocable in the cylindrical body 12 and is made of a predetermined diameter relative to the size of bore 34 of the body 12 whereby a predetermined leak down is provided between the outer peripheral surface of the plunger and the inner wall of the body 12. End 36 of the sleeve member 28 opposite end 32 thereof provides a fluid port or passage 37 adapted to be controlled by valve 18 and wherein one axial face of valve 18 is adapted to have axial bearing relation upon a valve seat 38 formed as an axial extension on sleeve 28.

Cage 20 is suitably fitted on reduced axial extension 40 of sleeve 28 and serves to confine valve 18 therein adjacent valve seat 38 for limited axial movement away from seat 38, the purpose of which will hereinafter appear. Cage 20 includes a radially outwardly extended annular flange 42 adapted to bear axially on an axial 1 shoulder of sleeve 28, an axially extended sleeve portion 44 for guiding the valve 28 in its axial movement, and a radially inwardly extended annular flange 46 which limits the axial extent of movement of valvelS away from valve seat 38. A passage 48 is provided centrally of flange 46 providing communication between valve chamber 50 and the bore 34 exteriorly of the cage 20.

Spring 22 is arranged in bore 34 intermediate the closed end of body 12 and flange 42 of cage 20 serving to hold the cage on the plunger and axially biasing the plunger outwardly of the body 12.

A fluid reservoir 59 provided centrally of sleeve member 28 has communication exteriorly thereof by way of passage 37 and a port 52 provided in the wall thereof. Port 52 is the way by which hydraulic fluid is supplied to the tappet for the operation thereof wherein an annular groove 54, on the outer periphery of the sleeve, communicates therewith and is adapted in turn to be continuously in communication with an annular groove 56, arranged in the internal peripheral wall of the body 12.

A port 58 arranged in the Wall of body 12 provides communication between the annular groove 56 and another annular groove 60 arranged on the outer peripheral surface of the body, whereby as hydraulic fluid is supplied from an external source, not shown, to groove 60,

it can pass in a continuous path through port 58, groove 56, groove 54, and port 52 to reservoir 50.

Cap members 30 comprises a main body portion 62 of a diameter slightly less than the diameter of the internal wall of the sleeve member in whose end 32 it is loosely fitted, an annular flange 64, one axial surface of which is adapted to axially abut the axial extremity of end 32 of the sleeve member and a socket 66 extending into the main body portion 62 thereof, within which a pushrod, not shown, is adapted to be received.

Cap member 30 is purposely made loose relative to sleeve member 28 and additionally is provided with ample clearance between the external periphery of its flange 64 and the internal peripheral surface of the body 12 so that the cap can move axially relative to sleeve 28 and thus permit of the passage of fluid from the reservoir 50 past the end 32 of sleeve 28 as necessity arises.

A controlled amount of lift loss can be provided in tappet by a physical proportioning of the basic elements thereof, that is by relating the areas of the plunger 16, valve 18 and port 37 and the axial travel of valve 18 to one another.

It has been determined that a direct relationship exists between lift loss and check valve travel for fiat check valves with the relationship being essentially a straight line, as plotted on the graph of Fig. 6, wherein lift loss is plotted against valve travel. Fig. 7 is a graph illustrating comparative lift loss-check valve curves wherein A is for a tappet having a plunger of .562" diameter, B is for a tappet having a plunger of .625" diameter and C is for a tappet having a plunger of .656" diameter. The check valves employed in the tappets of curves A, B and C each are of like diameter, that is .388. As such it will be noted that although the general slope of the curves A, B and C differ proportionately to the plunger diameter, a substantially straight line relationship is had between lift loss and check valve travel.

Because of the proven relationship existing between lift loss and check valve travel and the factors of plunger and check valve area entering therewith and further since it has been determined that lift loss is not materially aifected by oil viscosity, tappet position (all positions from horizontal to vertical), and annular clearance of the check valve up to certain predetermined valves, the following formula has been devised to predetermine lift loss for normal tappet operating conditions:

Cheek valve travel Plunger area X=approximately .27 with conventional circular or substantially circular check valves, and wherein check valve travel means the axial distance the valve is moveable away from the plunger and valve port; plunger area" means the cross-sectional area of the plunger at its maximum diameter; check valve area means the effective area on one face thereof; and valve port area means the area of the valve port at its point of communication with the tappet chamber.

It may be necessary to modify the value of X when unusually shaped flat check valves are used. However, it has been determined that only approximately a 4% deviation resulted from the use of .27 value of X wherein a valve having 4 radial arms or tangs was employed when the effective valve area was used for calculation purposes.

For all practical consideration the above formula can be used as the basis of design for fiat check valve hydraulic tappets of the general type represented by the drawings.

Although one specific design of hydraulic tappet has been disclosed and described, the formula devised is ap plicable to wide variety of hydraulic tappets employing free floating check valves just so long as the basic elements of structure are utilized in a like manner for a like purpose. Accordingly, the invention is to be limited by the appended claim as relates to the broad concepts herein illustrated and defined.

What I claim is:

A lift loss hydraulic tappet comprising a hollow cylinder having an open and a closed end, a plunger, reciprocable in the cylinder, having a passageway therethrough terminating at one end in a valve port, said port having communication with a chamber formed intermediate one end of the plunger and the closed end of the cylinder, and a flat valve supported for limited axial movement relative to the plunger, controlling communication between said chamber and said valve port, and wherein the area of the valve, the cross-sectional area of the plunger at its maximum diameter, the area of the valve port at its point of communication with the chamber and the valve travel are directly related to the lift loss of the tappet, with the following relation had among the area of the valve, the cross-sectional area of the plunger at its maximum diameter, the area of the valve port at its point of communication with the chamber, the valve travel and the lift loss of the tappet:

(Valve travel) Valve area Plunger area Lift loss Valve port area Valve area References Cited in the file of this patent 

